The present invention relates to designing method, a manufacturing method of a spectacle lens to correct eyesight, and a spectacle lens series.
In general, a spectacle lens is custom-made to meet the customer""s specification. However, it takes long time to process both front and back surfaces after receiving the customer""s order. Therefore, semifinished lens blanks whose front surfaces are finished are stockpiled and a back surface of the selected semifinished lens blank is processed according to the customer""s specification in order to shorten delivery times. Further, the entire range of available vertex power of a spectacle lens is divided into about ten sections, and one type of the semifinished lens blank is prepared for each of the sections.
Aspherical spectacle lenses whose at least one of the front and back surfaces is aspherical have come into wide use. When the spectacle lens employs an aspherical surface, the base curve becomes slower (i.e., the absolute value of the front vertex power decreases) and the maximum thickness becomes shorter as compared with a spherical lens whose both of the front and back surfaces are spherical. A conventional semifinished lens blank prepared for an aspherical spectacle lens has an aspherical finished front surface. A back surface thereof will be processed to be spherical or toric to meet the customer""s specification.
FIGS. 17A through 17C show a sample of the sections of the vertex power, FIG. 17A shows a range of minus diopter, FIG. 17B shows a range of plus diopter and FIG. 17C shows a range of mixed diopter. The entire range of the available vertex power, which is a combination of a spherical power SPH and a cylindrical power CYL, is divided into nine sections I through IX. Unit of each of powers is diopter and that is indicated by xe2x80x9cDxe2x80x9d in the following description. One type of the semifinished lens blank is prepared for each of the sections. The relationship between the sections and the base curves of the semifinished lens blank is shown in TABLE 1.
FIG. 18 shows surface powers of the front surfaces D1m(h) (unit: diopter) of the semifinished lens blanks prepared for the respective sections I to IX at the point whose distance from the optical axis of said finished lens is h (unit: mm) in a plane that contains the optical axis.
The sections of the vertex power are determined such that optical performances of the finished lenses that have the same front surface shape fall in an allowable range for every vertex power within the specific section. For instance, in the section II, which covers SPH xe2x88x925.25 D to xe2x88x927.00 D and CYL 0.00 D to xe2x88x922.00 D, the common aspherical surface whose base curve is 1.25 D is employed as the front surface and the back surface is processed to be a spherical surface whose surface power is xe2x88x927.25 D when the required vertex power is SPH xe2x88x926.00 D and CYL 0.00 D. Further, when the required vertex power is SPH xe2x88x927.00 D and CYL xe2x88x922.00 D, the back surface is processed to be a toric surface whose minimum and maximum surface powers are xe2x88x928.25 D and xe2x88x9210.25 D, respectively.
According to the conventional designing and/or manufacturing method, when the required vertex power is at the center of each section, an optical performance of the spectacle lens can be kept high. However, when the required vertex power is in periphery of each section, the optical performance is degraded.
For example, FIG. 19 shows graphs of astigmatisms with respect to the visual angle xcex2 of the spectacle lenses whose required vertex powers are SPH +3.25 D and +4.00 D that are in periphery of the section VIII. The section VXII covers SPH +3.25 D to +4.00 D and CYL 0.00 D to +2.00 D, the front surface of the semifinished lens blank prepared for this section is an aspherical surface whose base curve is +7.00 D. In each graph a solid line represents the astigmatism AS∞ for infinite object distance and a dotted line represents the astigmatism AS300 for object distance 300 mm. As shown in FIG. 19, the astigmatism AS300 is significant for the spectacle lens whose vertex power is SPH +3.25, while the astigmatism AS∞ is significant for the spectacle lens whose vertex power is SPH +4.00. Namely, the astigmatisms of the finished lenses (SPH +3.25 and SPH +4.00) are not balanced.
FIG. 20 shows average power error AP∞(30) at 30xc2x0 of visual angle for infinite object distance, astigmatism AS∞(30) at 30xc2x0 of visual angle for infinite object distance, and astigmatism AS300(30) at 30xc2x0 of visual angle for the object distance 300 mm of the spectacle lens series designed and manufactured by the conventional method within the entire range of vertex power SPH xe2x88x928.00 D to +5.00 D. As shown in FIG. 20, the aberrations significantly vary in each section and the degradations stand out at boundaries of the sections.
It is therefore an object of the present invention to provide a design method and a manufacturing method, which are capable of designing and manufacturing a spectacle lens having good optical performance for every vertex power.
For the above object, according to the designing method of the present invention, the entire range of available vertex power of a spectacle lens is divided into a plurality of sections, at least one type of semifinished lens blank whose one of the front and back surfaces is finished is prepared for each of the sections, one type of the semifinished lens blank is selected according to a required specification, and then an aspherical shape design for processing the unfinished surface of the selected semifinished lens blank is determined to be optimized for the required specification. The specification includes the vertex power and so on.
With this method, since the aspherical shape design for processing the unfinished surface of the lens blank is determined based on the required specification, a degree of flexibility in surface design becomes higher than the conventional method (an unfinished back surface of a lens blank whose front surface is finished as an aspherical surface is processed as a spherical or totic surface), which increases the optical performance of the finished lens regardless of whether the required vertex power is in the periphery in the specific section or in the center thereof.
In the following description, the surface of the finished lens that corresponds to the finished surface of the semifinished lens blank is referred to as a common surface that is common in the same section and the other surface of the finished lens that corresponds to the unfinished surface of the semifinished lens blank is referred to as a custom surface that is custom-made according to the required specification.
Further, the aspherical shape of the custom surface is optimized such that any pair of the finished lenses that have different vertex powers within the same section preferably satisfy the following condition (1) for at least one height h within the range of 0 less than h less than 15:
xcex94D1m(h)i+xcex94D2m(h)ixe2x89xa0xcex94D1m(h)j+xcex94D2m(h)jxe2x80x83xe2x80x83(1)
where
D1m(h) and D2m(h) are surface powers of the front and back surfaces (unit: diopter) at the point whose distance from the optical axis of said finished lens is h (unit: mm) in a plane that contains said optical axis,
xcex94D1m(h) is a variation of surface power of the front surface and is obtained by D1m(h)xe2x88x92D1m(0),
xcex94D2m(h) is a variation of surface power of the back surface and is obtained by D2m(h)xe2x88x92D2m(0), and
the subscripts xe2x80x9cixe2x80x9d and xe2x80x9cjxe2x80x9d represent the values of the finished lenses that have different vertex powers within the same section.
The condition (1) means xcex94D2m(h)ixe2x89xa0xcex94D2m(h)j when the front surface is a common surface. On the other hand, when the back surface is a common surface, the condition (1) means xcex94D1m(h)ixe2x89xa0xcex94D1m(h)j. In this manner, the variations of the surface powers of the custom surfaces are different from each other, which results in the spectacle lens having the optimum optical performance for every vertex power.
While the common surface may be either the front surface or the back surface, the front surface is preferably formed as the common surface to ease the manufacturing. It is preferable that the semifinished lens blank whose front surface is finished is prepared for each of the sections and the back surface is processed according to the required specification. That is, the following condition (2) is preferably satisfied:
D1m(h)i=D1m(h)j.xe2x80x83xe2x80x83(2)
When the front surface is formed as the common surface, it may be a spherical surface or a rotationally-symmetrical aspherical surface. In order to reduce the manufacturing cost, the front surface should be a spherical surface as defined in the following condition (3):
D1m(h)i=D1m(h)j=D1m(0)i=D1m(0)j. xe2x80x83xe2x80x83(3)
When the front surface is an aspherical common surface, the semifinished lens blanks described in the prior art can be employed. In either case, the aspherical shape of the back surface is determined such that the finished lens has the optimum optical performance.
Further, the aspherical shape of the custom surface preferably determined such that the finished lens satisfies the following condition (4) when Pi less than Pj less than xe2x88x923.00 and hxe2x89xa615:
MAX(|xcex94D1m(h)i+xcex94D2m(h)ixe2x88x92xcex94D1m(h)jxe2x88x92xcex94D2m(h)j |)xe2x89xa60.3xe2x80x83xe2x80x83(4)
where
P is a vertex power (unit: diopter); and
MAX( ) is a function that finds the maximum value in the specific section.
The condition (4) means that differences between the variations of the aspherical surface power of the finished minus lenses that have different vertex powers within the same section are not greater than 0.3 D when hxe2x89xa615.
On the other hand, the aspherical shape of the custom surface preferably determined such that the finished lens satisfies the following condition (5) when Pi greater than Pj greater than +2.00:
xcex94D1m(15)i+xcex94D2m(15)i less than xcex94D1m(15)j+xcex94D2m(15)j.xe2x80x83xe2x80x83(5)
Since the value of xcex94D1m(15)+xcex94D2m(15) is usually smaller than zero, the condition (5) means that the variation of the aspherical surface power increases as the plus vertex power becomes larger.
The aspherical shape of the custom surface is preferably optimized such that average power errors or astigmatisms of the finished lenses having different vertex powers within the same section are approximately balanced. Further, the aspherical shape of the custom surface is preferably optimized such that relationships between average power errors of astigmatisms of each finished lens within the same section are substantially the same.
For example, when the condition (6) is satisfied under Pi less than Pj and xcex2xe2x89xa630, the astigmatisms are well balanced.                               -          0.04                 less than                                                                               AS                  ∞                                ⁡                                  (                  β                  )                                                            i                ⁢                                  xe2x80x83                                                      +                                                            AS                  300                                ⁡                                  (                  β                  )                                            1                        -                                                            AS                  ∞                                ⁡                                  (                  β                  )                                            j                        -                                                            AS                  300                                ⁡                                  (                  β                  )                                            j                                            2            ⁢                          (                                                P                  i                                -                                  P                  j                                            )                                       less than         0.04                            (        6        )            
where
AS∞(xcex2) is astigmatism (unit: diopter) at visual angle xcex2 (unit: degree) for infinite object distance; and
AS300(xcex2) is astigmatism at visual angle xcex2 for object distance 300 mm)
The condition (6) means that differences of average values of astigmatisms for infinite and finite object distances are approximately identical for any pair of the finished lenses having different vertex powers within the same section. The difference of the average values of astigmatism is preferably smaller than 0.01 D for a pair of the finished lenses whose vertex powers are different in 0.25 D within the same section.
According to further example, when the condition (7) is satisfied under xcex2xe2x89xa630, the astigmatisms are well balanced.                               -          0.01                 less than                                                             AS                ∞                            ⁡                              (                β                )                                      +                                          AS                300                            ⁡                              (                β                )                                              2                 less than         0.1                            (        7        )            
The condition (7) means that average values of astigmatisms for infinite and finite object distances for each finished lens falls in the range of xc2x10.1.
According to still further example, when the condition (8) is satisfied when Pi less than Pj and xcex2xe2x89xa630, the average power errors are well balanced.                               -          0.04                 less than                                                                               AP                  ∞                                ⁡                                  (                  β                  )                                            1                        -                                                            AP                  ∞                                ⁡                                  (                  β                  )                                            j                                                          P              i                        -                          P              j                                       less than         0.04                            (        8        )            
where
AP∞(xcex2) is average power error at visual angle xcex2 (unit: degree) for infinite object distance.
The condition (8) means that differences of, average power errors for the infinite object distance are approximately identical for any pair of the finished lenses having different vertex powers within the same section. The difference of the average power error is preferably smaller than 0.01 D for a pair of the finished lenses whose vertex powers are different by 0.25 D within the same section.
According to yet further example, when the condition (9) is satisfied under xcex2xe2x89xa630, the average power errors are well balanced.
xe2x88x920.1 less than AP∞(xcex2) less than 0.1xe2x80x83xe2x80x83(9)
The condition (9) means that the average power error for the infinite object distance for each finished lens falls in the range of xc2x10.1.
On the other hand, the spectacle lens series according to the present invention includes a plurality of types of spectacle lenses that are different in vertex power. One of said front and back surfaces of each spectacle lens is predetermined for each of sections, which is defined to divide the entire range of available vertex power, the other surface is an aspherical surface determined for a required specification. Further, the condition (1) described above is satisfied. In such a case, the front surface may be the common surface and it may be a spherical surface.